The present invention relates to a light guide and in particular, a light guide for medical instruments.
Light guides are used in medicine, e.g. for instruments for laser operations or for endoscopes. In this case, the light guide consists of a feeding unit, a light guide fiber and a casing tube surrounding the fiber at a distance. The light guide fiber itself consists of the light guide core, e.g. of quartz glass, a silicone layer around tne light guide core and a polytetrafluoroethylene jacket.
The feeding unit is used to feed the light or laser radiation focused into the light guide fiber. The light guide fiber and casing tube are mounted in the feeding unit for this purpose. At the other end of the light guide, the light guide fiber is mounted directly in the casing tube.
The casing tube construction varies, depending on the intended application. For example, it may be a relatively thin, flexible, gas- or liquid-tight tube through which gas or liquid is fed by the feeding unit to the front end of the light guide fiber and which cools this end. Such light guides are suitable for use in flexible or rigid instruments.
Relatively rigid and voluminous casing tubes are also known, which consist, if needed, of several tubes, e.g. a gas-tight tube and a protective tube with a relatively thick wall surrounding the former. This protective tube system serves as protection against breaking or damage for the light guide, which is exposed or built into a rigid instrument. Gas and liquid protection is generally not required for the outer protective tube.
When the light guide is bent, stresses build up between the individual parts of the light guide, which cause tensile forces in the longitudinal direction toward the light guide fiber and its light guide core, which is longitudinally rigid. Especially when the light guide, which is up to three meters long, is rolled up for transporting or for other non-use, these stresses can become so great, due to the different radii of casing tube or casing tube system and light guide fiber with light guide core, that the light guide fiber or the light guide core is shifted in one of the mounting sites. When this occurs at the mounting site within the current feeding unit, the focusing of the light radiation to be fed is disturbed. The light guide fiber or the light guide core can be thermally damaged as well. If the light guide fiber or the light guide core shifts at the other mounting site, the light guide fiber or the light guide core can easily be damaged there. When the light guide core is also cooled with gas or liquid, the cooling is weakened by the shift, the light guide core becomes excessively hot and possibly useless.
One could think of mounting the light guide fiber with the light guide core with greater force, to prevent the longitudinal shifting of the light guide core. But this is possible only to a limited extent, if the optical properties of the light guide fiber are not to be impaired by the pressure. For example, the soft silicone layer inserted between light guide core and polytetrafluoroethylene jacket should not be damaged, since this serves as a light refractive barrier layer for the light rays within the light guide core. This alone makes an increase in the mounting force at will impossible.